Transaminase mutant and application thereof

ABSTRACT

The invention provides a transaminase mutant and application thereof, wherein the amino acid sequence of the transaminase mutant is formed after mutation of the amino acid sequence as shown in SEQ ID NO: 1, and mutated amino acid sites comprise T7C+S47C sites. The transaminase mutant having the mutation sites can be further prepared into an immobilized enzyme through an immobilization technology, the immobilized enzyme has relatively high activity and high stability, can be recycled for multiple times, and is applicable to continuous flow reaction in a packed bed.

TECHNICAL FIELD

The invention relates to the field of enzyme engineering, in particular to a transaminase mutant and application thereof.

BACKGROUND

ω-transaminase (ω-TA) belongs to transferases and catalyzes the exchange of an amino group with a keto group like other transaminases. In most cases ω-transaminase refers to a class of enzyme, as long as the substrate or product of the reaction does not contain α-amino acid in an enzyme-catalyzed transamination reaction, the enzyme can be called ω-transaminase. ω-transaminases can efficiently produce chiral amines by stereoselective transamination using ketones as raw materials. Enantiomeric chiral amines are key intermediates for many pharmaceutical compounds with broad biological activity (ChemBioChem. 9, 2008, 363-365, Chem. Commun. 46, 2010, 5569-5571, Biotechnol. Bioeng. 108, 2011, 1479-1493). Because of the relatively cheap substrate and high purity of the product, it has attracted more and more attention from researchers (Green Chemistry, 2017, 19, 2: 333-360). And transaminases have shown promise for the production of chiral amines (Organic Process Research & Development, 2010, 14, 234-237).

Although much attention has been paid to the progress in producing chiral amines with transaminase, there are many problems in the application of enzymatic methods in scale-up production. For example, low enzyme activity and large amount of enzyme lead to the increase of fermentation cost, and are easy to be denatured and inactivated by the influence of organic solvents in the reaction system.

In addition, in the process of separating the product amine, the enzyme can only be denatured and inactivated to form precipitation and then removed and discarded, which cannot be reused, or the product is extracted from the aqueous solution with organic solvent, and the enzyme continues to exist in the aqueous solution, but at this time, due to the influence of many harsh conditions such as pH and solvent, the enzyme is inactivated and cannot be used again.

In the prior art, it has been reported that the enzyme is immobilized by immobilization technology to improve the recovery and reuse of the enzyme. However, at present, there are many researches on immobilization technology in the fields of lipase, penicillin acylase, amylase and others, because these enzymes have better stability than other enzymes, and the loss of enzyme activity after immobilization is lower. For most transaminases, the stability is poor, especially when an organic phase exists in the system, the loss of enzyme activity is easily to be caused in an immobilization operation process, so there is less research on the immobilization of transaminase and the research on immobilized transaminase suitable for continuous reaction is even less.

As for the transaminase capable of catalyzing the amino conversion reaction of the following substrate 1 and substrate 2, if the reaction is catalyzed by the free transaminase, the free enzyme cannot be recovered and can only be used once. In addition, due to the existence of enzyme protein in the reaction system, the post-treatment emulsification phenomenon is extremely serious, and the product separation is difficult.

If the used transaminase is immobilized, the recovery and utilization of the enzyme can be realized theoretically, but the enzyme activity recovery is still low after the existing transaminase used for catalyzing the substrate 1 or the substrate 2 is immobilized. Moreover, since most of the existing substrate ketones (amino receptors) are poorly water-soluble, the continuous reaction cannot be carried out in a pure aqueous phase. In order to realize the continuous reaction, enough organic co-solvent needs to be added to dissolve the substrate, but the existing transaminase has poor tolerance to temperature, pH and organic solvent, and the organic solvent can easily inactivate the transaminase. It is thus difficult to realize its immobilization treatment.

Therefore, it is necessary to improve the existing transaminases which can catalyze the above substrates in order to improve their poor stability and limited application in extreme environments including organic solvents.

SUMMARY

The invention mainly aims to provide a transaminase mutant and application thereof, so as to solve the problem that the application is limited due to poor tolerance of the transaminase activity in an extreme environment in the prior art.

To achieve the above object, according to one aspect of the present invention, a transaminase mutant is provided, the transaminase mutant has a sequence in which an amino acid mutation occurs in the sequence shown in SEQ ID NO: 1, and sites of the amino acid mutation comprise T7C+S47C.

Further, the sites of the amino acid mutation further comprise any one or more of the following: M356L, F364L, C404L, M430L, R405E/A, K90G, K219T, K304D, K51R, A95P, E368P, Q346E, H333K, D371G, E246A, C328A, N412G, T402P, T107F/A, G110P, K69N, G201C, Q380L, K193I, I297L, R305H, F111Y, K190E and A286T, wherein “/” represents “or”.

Further, the sites of the amino acid mutation further include any one of the following combined mutation sites: K51R+W187Y, R405E+A95P, R405E+A95P+K304D, R405E+A95P+K304D+Q380L, R405E+K90G+A95P+K304D+Q380L, R405E+K90G+A95P+K304D+Q380L+E368P, R405E+K90G+A95P+K304D+Q380L+Q346E, R405E+K90G+A95P+K304D+Q380L+H333K, R405E+K90G+A95P+K304D+Q380L+D371G, R405E+K90G+A95P+K304D+Q380L+E246A, R405E+K90G+A95P+K304D+Q380L+C328A, R405E+K90G+A95P+K304D+Q380L+N412G, R405E+K90G+A95P+K304D+Q380L+T402P, R405E+K90G+A95P+K304D+Q380L+T107F, R405E+K90G+A95P+K304D+Q380L+T107A, R405E+K90G+A95P+K304D+Q380L+G110P, R405E+K90G+A95P+K304D+Q380L+1297L, R405E+K90G+A95P+K304D+Q380L+1297L+E368P+T107A, R405E+K90G+A95P+K304D+Q380L+1297L+A286T R405E+K90G+A95P+K304D+Q380L+1297L+E368P R405E+K90G+A95P+K304D+Q380L+1297L+E368P+T107A+K69N, R405E+K90G+A95P+K304D+Q380L+1297L+E368P+T107A+G201C and R405E+K90G+A95P+K304D+Q380L+1297L+E368P+T107A+A286T.

To achieve the above object, according to the second aspect of the present invention, a DNA molecule encoding any one of the transaminase mutants described above is provided.

According to the third aspect of the present invention, a recombinant plasmid having linked thereto any of the DNA molecules described above is provided.

According to the fourth aspect of the present invention, an immobilized transaminase comprising any one of the transaminase mutants described above is provided.

Further, the immobilized transaminase is a transaminase crosslinked enzyme aggregate of the transaminase mutant; preferably, the transaminase mutant is precipitated to obtain a transaminase aggregate, and a free amino, a phenolic, an imidazolyl, or a sulfhydryl group in the transaminase aggregate is further crosslinked with a cross-linking agent to obtain the transaminase cross-linked enzyme aggregate, wherein the cross-linking agent is selected from any one of glutaraldehyde, N, N-methylene bisacrylamide, bismaleimide and dextran; preferably, the transaminase cross-linked enzyme aggregate is a cross-linked enzyme aggregate of a transaminase mutant containing the following amino acid mutation sites on the basis of the amino acid sequence shown in SEQ ID NO:1: T7C+S47C, T7C+S47C+A95P, T7C+S47C+R405E+K90G+A95P+K304D+Q380L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+K69N, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+H333K, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+E368P, T7C+S47C+K51R+W187Y, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+Q346E, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+C328A and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L; preferably, the dextran has a molecular weight of 6 KDa-200 KDa; preferably, the transaminase aggregate is obtained by ethanol precipitation of the transaminase mutant; preferably, a free amino group in the transaminase aggregate is cross-linked with glutaraldehyde to obtain transaminase cross-linked enzyme aggregates.

Further, the immobilized transaminase is a transaminase embedded-crosslinked immobilized enzyme; preferably, the transaminase embedded-crosslinked enzyme is an embedded-crosslinked immobilized enzyme of the transaminase mutant containing the following amino acid mutation sites on the basis of the amino acid sequence shown in SEQ ID NO: 1: T7C+S47C, T7C+S47C+R405E+K90G+A95P+K304D+Q380L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+Q346E and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L; preferably, a free amino group in the transaminase mutant form a Schiff base by crosslinking with glutaraldehyde to obtain a transaminase cross-linked enzyme, and the transaminase cross-linked enzyme is embedded into a polyacrylamide gel grid to obtain the transaminase embedded-crosslinked immobilized enzyme.

Further, the immobilized transaminase is a covalent immobilized enzyme of which the transaminase mutant is covalently connected with the carrier; preferably, the covalently immobilized enzyme is a covalently immobilized enzyme of a transaminase mutant containing the following amino acid mutation site s on the basis of the amino acid sequence shown in SEQ ID NO:1: T7C+S47C, T7C+S47C+A95P, T7C+S47C+Q380L, T7C+S47C+R405E, T7C+S47C+K51R+W187Y, T7C+S47C+R405E+A95P+K304D, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+E368P, T7C+S47C+R405E+K90G+A95P+K304D+Q380L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+H333K, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T; preferably, the carrier is a chitosan carrier and a resin carrier; more preferably, the chitosan carrier is covalently bound to the transaminase mutant by a hydroxyl and/or an amino group to form the covalent immobilized enzyme; more preferably, the resin carrier comprises a matrix and a functional group linked with the matrix, wherein the matrix is selected from any one of copolymers of styrene and methacrylate, polystyrene resins and polymethacrylate resins, and the functional group linked with the matrix is selected from a C2 short-chain amino group, a C4 medium-chain amino group, a C6 long-chain amino group or a epoxy group; further preferably, the resin carrier is selected from ECR8309, ECR8315, EC-HFA, LX-1000HA, LX-1000EA, ECR8409, ECR8415, EC-EP, ECEP403, EXE119, LX-1000EP, Immobead-150A, Immobead-150P, Immobead350A, ECR8206, ECR8209, ECR8215 or ECR8285.

Further, the immobilized transaminase is a chelating immobilized enzyme formed by chelating a transaminase mutant and a carrier through metal ions; preferably, the chelating immobilized enzyme is a chelating immobilized enzyme of a transaminase mutant containing the following amino acid mutation site s on the basis of the amino acid sequence shown in SEQ ID NO:1: T7C+S47C, T7C+S47C+A95P, T7C+S47C+R405E+K90G+A95P+K304D+Q380L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+G201C and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T; preferably, the carrier is a porous glass carrier; further preferably, the porous glass carrier is EziG-101, EziG-102 or EziG-103.

Further, the immobilized transaminase is an adsorption immobilized enzyme formed by the transaminase mutant and the carrier through physical adsorption; preferably, the adsorption immobilized enzyme is a covalent immobilized enzyme of a transaminase mutant containing the following amino acid mutation site s on the basis of the amino acid sequence shown in SEQ ID NO:1: T7C+S47C, T7C+S47C+A95P, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+H333K, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+Q346E, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+N412G, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+G201C; preferably, the carrier is a resin carrier; more preferably, the resin carrier comprises a matrix and a functional group connected with the matrix, the matrix is selected from any one of a styrene and methacrylate copolymer, a polystyrene resin and a polymethacrylate resin, and the functional group connected with the matrix is an octadecyl; further preferably, the resin carrier is selected from ECR8806, ECR1030, ECR1090, ECR1061, ECR1091, ECR8804, Immobead-EC1, Immobead-5605, Immobead-5861, X1750409, EXE120 or Diaion HP2MG.

According to the fifth aspect of the present invention, a method for producing a chiral amine is provided, comprising the step of transamination reaction between a ketone compound and an amino donor catalyzed by a transaminase, wherein the transaminase is any one of the transaminase mutants above or any one of the immobilized transaminases above.

Further, the transaminase is any one of the transaminase mutants, and the method is a batch reaction; preferably, the reaction system of the batch reaction is an aqueous phase reaction system.

Further, the transaminase is any immobilized transaminase, and the method is a continuous reaction; preferably, the reaction system of the continuous reaction is an organic phase reaction system.

Further, the ketone compound is

wherein R1 and R2 are each independently C1-C8 alkyl, C5-C10 cycloalkyl, C6-C10 aryl, or C5-C10 heteroaryl, or R1 and R2 together with the carbon on the carbonyl form a C5-C10 heterocyclyl, a C5-C10 carbocyclyl or a C5-C10 heteroaryl, the heteroatoms in the C5-C10 heterocyclyl and C5-C10 heteroaryl are each independently selected from at least one of nitrogen, oxygen and sulfur, the aryl in the C6-C10 aryl, the heteroaryl in the C5-C10 heteroaryl, the carbocyclyl in the C5-C10 carbocyclyl, or the heterocyclyl in the C5-C10 heterocyclyl is each independently unsubstituted or substituted with at least one of halogen, alkoxy or alkyl, preferably, the ketone compound is

and the transamination reaction product is

preferably, the amino donor is isopropyl amine.

According to the technical scheme provided by the invention, a series of transaminase mutants with greatly improved enzyme activity and/or stability are screened by performing directional evolution on the transaminase of the amino acid sequence shown in SEQ ID NO: 1, wherein the amino acid sequence of the mutants is an amino acid sequence which is mutated on the basis of the amino acid sequence shown in SEQ ID NO: 1, and the mutated amino acid sites comprise the T7C+S47C sites. The transaminase mutant containing the mutation sites above can be applied in a relatively extreme environment.

DETAILED DESCRIPTION OF THE INVENTION

It should be noted that the examples and features in the examples herein may be combined with one another without conflict. The present invention will be described in detail below in combination with the examples.

Term Explanation

Site-directed mutagenesis: refers to the introduction of desired changes (usually characterizing changes in favorable directions) to the target DNA fragments (either genomes or plasmids) by polymerase chain reaction (PCR), including addition, deletion, point mutation, etc. of bases. Site-directed mutagenesis can rapidly and efficiently improve the properties and characterization of target proteins expressed by DNA, and is a very useful means in gene research.

The introduction of site-directed mutation by whole plasmid PCR is simple and effective, and is a widely used method at present. The principle is as follows: a pair of primers containing mutation sites (forward and reverse), and the template plasmid is annealed, then “cycled extended” by polymerase, the so-called cyclic extension means that the polymerase extends the primers according to the template, and then returns to the 5′ end of the primers after a circle, after cycles of repeated heating and annealing, this reaction is different from rolling circle amplification, will not form multiple tandem copies. The extension products of the forward primer and the reverse primer are annealed and paired to form a nicked open circular plasmid. Dpn I digests the extension product, since the original template plasmid is derived from conventional Escherichia coli (E. coli), subjected to dam methylation modification and sensitive to Dpn I, it is chopped, and the plasmid with the mutant sequence synthesized in vitro is not cut due to no methylation, so that the plasmid is successfully transformed in subsequent transformation, and clones of the mutant plasmid can be obtained. The mutant plasmid is transformed into a host cell to induce the target protein to be expressed.

Error-prone PCR: refers to the PCR under error-prone conditions, is a PCR technique that is easy to cause errors in copied DNA sequences, also known as mismatch PCR or error prone PCR. In particular, it refers to a method of inducing DNA sequence variation in vitro with low fidelity TaqDNA polymerase and changing PCR reaction conditions, reducing the fidelity of DNA replication and increasing base mismatch in the process of new DNA chain synthesis, resulting in more point mutations in the amplified products.

Error-prone PCR is the most simple and effective technique for gene random mutagenesis in vitro. Its principle is that base isomerization provides the possibility of mismatch. Tautomers are appeared in all the four bases that make up DNA, wherein three oxygen-containing base guanine (G), cytosine (C) and thymine (T), have two tautomers of keto form and enol form. The two nitrogen-containing bases, adenine (A) and thymine, have an amine form and an imine form. G, C and T exist mainly in a keto form structure, the ratio of the enol form structure is extremely low, and the nitrogen atoms on the nitrogen-containing bases A and T mainly exist in an amino (NH₂) state, and the ratio of the nitrogen atoms in the imine (NH) state is extremely low. The different positions of hydrogen atoms between different isomers and the different deviation directions of electron clouds at the same position can change the pairing forms of bases, so that mismatches can occur on the replicated sub-chains. For example, when thymine is present in a keto form structure, paired with adenine, and when thymine in an enol form structure, paired with guanine, thus giving rise to an unstable base pair in which A can be matched with C and T can be matched with G, resulting in a mismatch.

Among several known thermo-tolerance DNA polymerases, TaqDNA polymerase has the highest mismatch rate. TaqDNA polymerase has the highest activity among the found thermo-tolerance DNA polymerases. It has 5′-3′ exonuclease activity, but not 3′-5′ exonuclease activity, therefore, it has no correction function for some mononucleotide mismatches during synthesis, so it has a higher probability of mismatch than DNA polymerases with 3′-5′ correcting activity. The fidelity of DNA polymerases can be reduced by a variety of methods, including using four dNTPs of different concentrations, adding Mn²⁺, increasing Mg²⁺ concentration, etc. Several mutagenesis methods lead to different mechanisms of base variation in amplified DNA chain. MnCl₂ is a mutagenic factor of DNA polymerases, adding Mn²⁺ can reduce the specificity of polymerase to template and improve the mismatch rate; the unbalance of the concentrations of the four dNTPs can improve the probability of base misincorporation and realize mismatch; Mg²⁺ has the function of activating Taq enzyme, increasing the concentration of Mg²⁺ to exceed the normal dosage can stabilize the non-complementary base pairs; increasing the dosage of TaqDNA polymerase and the extension time of each cycle can increase the probability of mismatch terminal extension; decreasing the initial template concentration will increase the proportion of variant templates in the following PCR cycle.

Immobilized enzyme: refers to an enzyme whose catalysis can be repeatedly and continuously used within a certain space range. Generally, enzyme catalyzed reaction is carried out in aqueous solutions, whereas immobilized enzymes are physically or chemically treated to render water-soluble enzymes insoluble but still enzymatically active. After immobilization, the general stability of enzyme is increased, it is easy to separate from the reaction system, easy to control, can be used many times, easy to transport and store and is favorable to automatic production, but the activity and the use range is reduced.

Immobilized enzyme carrier matrix: refers to a material that forms the backbone of an immobilized enzyme carrier.

As used herein, 1 wt refers to 1 g of transaminase mutant recombinant wet cells required to transform 1 g of substrate.

In the present application, the 1V referred to is equal to the volume of the reaction system/mass of the substrate.

In order to solve the problem that the application is limited due to poor tolerance of transaminase activity in an extreme environment in the prior art, a typical embodiment of the application carries out directed evolution on the transaminase which is mutated at the R416T site from the Chromobacterium violaceum to obtain the transaminase mutant, wherein the transaminase mutant has a sequence in which an amino acid mutation occurs in the sequence shown in SEQ ID NO: 1; the site at which the amino acid mutation occurs includes the T7C+S47C site. In the relatively extreme environment, the mutational transaminase activity of the transaminase with mutation occurs at R416T+T7C+S47C site was significantly higher than that of the R416T mutant.

Hereinafter, the above technical solutions and effects will be described with reference to experiments.

I. Screening of Mutants with Improved Tolerance to Extreme Environments

The transaminase derived from the Chromobacterium violaceum was modified in the present invention to obtain the R416T mutant with improved enzyme activity, and the amino acid sequence of the R416T mutant is shown in SEQ ID NO: 1. The activity of the enzyme is good, but its stability is not ideal. In order to improve the stability of the enzyme, five groups of double-point mutations Q78C+A330C, V137C+G313C, A217C+Y252C, T7C+S47C and L295C+328C were designed with the R416T mutant as the template, and a primer sequence was designed with a QuikChange Primer Design webpage. The mutant site was introduced into the mutant R416T by whole plasmid PCR, and the mutant plasmid with new mutation site was obtained with pET-22b(+) as the expression vector.

The mutant plasmid was transformed into E. coli cells and induced overnight under the optimal conditions of transaminase-induced expression at 25° C. and 0.1 mM IPTG, and then the crude enzyme was obtained by ultrasonication of the cells. After the enzyme solution expressed by the mutant strain was treated for 1 h in the extreme environment of 45-50° C., pH 9.5 and 20% DMSO, substrate 1 or substrate 2 was added, and the enzyme amount of 1 wt was used to continue to react under this condition for 16 h, and then the transformation rate was detected. The mutant with improved stability was screened by this method, in which the activity of the mutant (R416T+T7C+S47C) at T7C+S47C sites was significantly higher than that of the R416T mutant. Under this condition, the transformation rate catalyzed by R416T was 15%, while that catalyzed by mutant R416T+T7C+S47C was 72%.

Furthermore, using the R416T+T7C+S47C mutant as the female parent, 33 pairs of site-directed mutagenesis (specific primers designed by QuikChange Primer Design web page) (M356L, w360L, F364L, C404L, M430L, M438L, C445A, F449V, R405E, R405A, K90G, K190R, K219T, K304D, K51R, W187Y, K193E, K143R, N151M, S8P, A33P, A95P, E368P, Q346E, H333K, D371G, E246A, C328A, N412G, T402P, T107F, T107A, G110P), the primer sequences were designed by QuikChange Primer Design web page, and the mutant plasmid with target gene was obtained by site-directed mutagenesis with pET-22b (+) as expression vector. The mutant plasmid was transformed into E. coli cells and induced overnight under the optimal conditions of transaminase-induced expression at 25° C. and 0.1 mM IPTG. Then the crude enzyme was obtained by ultrasonication of the cells.

After the enzyme solution expressed by the mutant strain was treated for 1 h in the extreme environment of 30-45° C., pH 9.5-10 and 50% DMSO, substrate 1 or substrate 2 was added, and continued to react under this condition for 16 h, and then the transformation rate was detected. Mutants with enhanced tolerance to temperature, pH and organic solvent were screened in this manner. The screen results are: the tolerance of the mutant with mutation site at M356L, F364L, C404L, M430L, R405E, R405A, K90G, K219T, K304D, K51R, A95P, E368P, Q346E, H333K, D371G, E246A, C328A, N412G, T402P, T107F, T107A, G110P to the environment of 30° C., pH9.5 and 50% DMSO was 8%-40% higher than that of R416T+T7C+S47C mutant. The tolerance of some mutants to the environment of 45° C., pH 9.5, 50% DMSO was 1.7-2.1 times higher than that of R416T+T7C+S47C mutant, and the tolerance of some mutants to the environment of 40° C., pH 10, 50% DMSO was 3.7-3.9 times higher than that of R416T+T7C+S47C mutant.

With the R416T+T7C+S47C mutant as the female parent, specific mutants with improved tolerance under different extreme environments were screened by site-directed mutagenesis as shown in Table 1 and Table 2 below.

TABLE 1 single point mutants with improved tolerance to the environment of 30° C., pH 9.5, 50% DMSO obtained by site-directed mutagenesis. Degree of Degree of Degree of tolerance Mutation tolerance Mutation tolerance Mutation site improvement site improvement site improvement Female parent No D371G 23% T107F 36% R416T + T7C + S47C K90G  8% T402P 25% E368P 43% K219T  9% R405A 27% C328A 39% M430L 13% E246A 29% T107A 39% K51R 14% H333K 30% R405E 41% C404L 16% A95P 31% N412G 19% M356L 18% G110P 32% Q346E 35% F364L 18% K304D 34% −/− −/−

TABLE 2 single point mutants with improved tolerance to the environment of 40° C., pH 10, 50% DMSO obtained by site-directed mutagenesis. Degree of Degree of Degree of tolerance Mutation tolerance Mutation tolerance Mutation site improvement site improvement site improvement R416T + T7C + No C328A 312% A95P 387% S47C G110P  98% D371G 286% Q346E 409% H333K 377% T402P 326% E368P 421% T107A 342% T107F 339% R405E 369% E246A 253% −/− −/− −/− −/−

In order to simply and effectively screen more ideal mutants, the R416T+T7C+S47C mutant is randomly mutated by adopting an error-prone PCR technology in the present invention.

In this application, the target gene fragment was linked to the pET-22b vector by error-prone PCR method, and mutant plasmid with the target gene was obtained. The mutant plasmid was transformed into E. coli cells and induced overnight under the optimal conditions of transaminase-induced expression at 25° C. and 0.1 mM IPTG. Finally, the crude enzyme was obtained by ultrasonication of the cells.

After the enzyme solution expressed by the mutant strain was treated for 1 h in the extreme environment of 30-45° C., pH9-10 and an organic solvent concentration of 50% DMSO or 35% MeOH, substrate 1 or substrate 2 was added, and continued to react under this condition for 16 h, then the transformation rate was detected. Mutants with enhanced tolerance to temperature, pH and organic solvents were screened in this manner. The screen results showed that the tolerance of the mutant with mutation site at K69N, G201C, Q380L, K193I, I297L, R305H, F111Y, K190E, A286T to the environment of 30° C., pH 9.5 and 50% DMSO was 16%-45% higher than that of R416T+T7C+S47C mutant. The tolerance of some mutants to the environment of 40° C., pH 10, 50% DMSO was 117%-537% higher than that of R416T+T7C+S47C mutant, and the tolerance of some mutants to the environment of 30° C., pH 8, 35% MeOH was 233%-649% higher than that of female parent.

With the R416T+T7C+S47C mutant as the female parent, specific mutants with improved tolerance under different extreme environments were screened by error-prone PCR as shown in Table 3 to Table 5 below.

TABLE 3 single point mutants with improved tolerance to the environment of 30° C., pH 9.5, 50% DMSO obtained by error-prone PCR. Degree of Degree of tolerance tolerance Mutation site improvement Mutation site improvement R416T + T7C + No K193I 38% S47C F111Y 16% K190E 31% Q380L 41% R305H 43% I297L 42% A286T 45% K69N 24% G201C 28%

TABLE 4 single point mutants with improved tolerance to the environment of 40° C., pH 10, 50% DMSO obtained by error-prone PCR. Degree of Degree of tolerance tolerance Mutation site improvement Mutation site improvement R416T + T7C + No Q380L 509% S47C K190E 191% K193I 312% F111Y 238% I297L 537% R305H 174% K190E 191% K69N 124% G201C 117%

TABLE 5 single point mutants with improved tolerance to the environment of 30° C., pH 8, 35% MeOH obtained by error-prone PCR Degree of Degree of tolerance tolerance Mutation site improvement Mutation site improvement R416T + T7C + No R305H 497% S47C F111Y 233% I297L 576% K190E 403% K193I 579% A286T 623% Q380L 649% K69N 288% G201C 294%

In order to further evolve transaminases with better stability and tolerance, in the present invention, the sites with improved stability and tolerance of the transaminases are subjected to multi-point combined mutation, and then the multi-point mutants with further improved stability and tolerance are obtained by a directed screening method.

Mutation sites for combined mutations were from K51R, W187Y, R405E, K90G, A95P, K304D, Q380L, E368P, Q346E, H333K, D371G, E246A, C328A, N412G, T402P, T107F, T107A, G110P, I297L, K69N, G201C and A286T.

The combined mutation is any combination of these sites. In particular, the combined mutation include, but are not limited to the following: K51R+W187Y, R405E+A95P, R405E+A95P+K304D, R405E+A95P+K304D+Q380L, R405E+K90G+A95P+K304D+Q380L, R405E+K90G+A95P+K304D+Q380L+E368P, R405E+K90G+A95P+K304D+Q380L+Q346E, R405E+K90G+A95P+K304D+Q380L+H333K, R405E+K90G+A95P+K304D+Q380L+D371G, R405E+K90G+A95P+K304D+Q380L+E246A, R405E+K90G+A95P+K304D+Q380L+C328A, R405E+K90G+A95P+K304D+Q380L+N412G, R405E+K90G+A95P+K304D+Q380L+T402P, R405E+K90G+A95P+K304D+Q380L+T107F, R405E+K90G+A95P+K304D+Q380L+T107A, R405E+K90G+A95P+K304D+Q380L+G110P, R405E+K90G+A95P+K304D+Q380L+I297L, R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A, R405E+K90G+A95P+K304D+Q380L+I297L+A286T, R405E+K90G+A95P+K304D+Q380L+I297L+E368P, R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+K69N, R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+G201C and R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T.

The mutant plasmid was transformed into E. coli cells and induced overnight under the optimal conditions of transaminase-induced expression at 25° C. and 0.1 mM IPTG. Then the crude enzyme was obtained by ultrasonication of the cells.

After the enzyme solution was treated for 1 h in more extreme environment of 45° C., pH 9.5-10 and containing 50% DMSO or 35% MeOH, substrate 1 was added, and continued to react under this condition for 16 h, then the transformation rate was detected. The tolerance of some combined mutants to the environment of 40° C., pH 10, 50% DMSO was 231%-610% higher than that of the female parent, the tolerance of some combined mutants to the environment of 30° C., pH 8, 35% MeOH was 213%-990% higher than that of the female parent, and the tolerance of some combined mutants to the environment of 45° C., pH 8, 40% MeOH was 3000% higher than that of the female parent. Specific combined mutants with improved tolerance are shown in Tables 6 to 8 below.

TABLE 6 combined mutants with improved tolerance to the environment of 40° C., pH 10, 50% DMSO. Degree of Degree of tolerance tolerance Mutation site improvement Mutation site improvement R416T + T7C + No R405E + A95P 231% S47C K51R + W187Y 507% R405E + K90G + 298% A95P + K304D + Q380L + E246A R405E + A95P + 572% R405E + K90G + 334% K304D A95P + K304D + Q380L + C328A R405E + A95P + 562% R405E + K90G + 246% K304D + Q380L A95P + K304D + Q380L + N412G R405E + K90G + 586% R405E + K90G + 323% A95P + K304D + A95P + K304D + Q380L Q380L + T402P R405E + K90G + 611% R405E + K90G + 498% A95P + K304D + A95P + K304D + Q380L + E368P Q380L + T107F R405E + K90G + 552% R405E + K90G + 573% A95P + K304D + A95P + K304D + Q380L + Q346E Q380L + T107A R405E + K90G + 563% R405E + K90G + 317% A95P + K304D + A95P + K304D + Q380L + H333K Q380L + G110P R405E + K90G + 368% R405E + K90G + 610% A95P + K304D + A95P + K304D + Q380L + D371G Q380L + I297L

TABLE 7 combined mutants with improved tolerance to the environment of 30° C., pH 8, 35% MeOH. Degree of Degree of tolerance tolerance Mutation site improvement Mutation site improvement R416T + T7C + No R405E + K90G + 783% S47C A95P + K304D + Q380L + C328A R405E + K90G + 213% R405E + K90G + 837% A95P + K304D + A95P + K304D + Q380L + D371G Q380L + T107A R405E + K90G + 288% K51R + W187Y 866% A95P + K304D + Q380L + T402P R405E + K90G + 354% R405E + K90G + 925% A95P + K304D + A95P + K304D + Q380L + N412G Q380L + E368P R405E + K90G + 557% R405E + K90G + 979% A95P + K304D + A95P + K304D + Q380L Q380L + I297L + E368P + T107A R405E + K90G + 773% R405E + K90G + 990% A95P + K304D + A95P + K304D + Q380L + Q346E Q380L + I297L R405E + K90G + 783% R405E + K90G + 697% A95P + K304D + A95P + K304D + Q380L + H333K Q380L + I297L + E368P + T107A + A286T R405E + K90G + 596% R405E + K90G + 623% A95P + K304D + A95P + K304D + Q380L + I297L + Q380L + I297L + E368P + T107A + E368P + T107A + K69N G201C

TABLE 8 combined mutants with increased tolerance to the environment of 45° C., pH 8, 40% MeOH. Degree of Degree of tolerance tolerance Mutation site improvement Mutation site improvement R416T + T7C + No R405E + K90G + 3090% S47C A95P + K304D + Q380L + I297L + A286T R405E + K90G + 3100% R405E + K90G + 3000% A95P + K304D + A95P + K304D + Q380L + I297L Q380L + I297L + E368P R405E + K90G + 2889% R405E + K90G + 2927% A95P + K304D + A95P + K304D + Q380L + I297L + Q380L + I297L + E368P + T107A + E368P + T107A + K69N G201C R405E + K90G + 3010% R405E + K90G + 2996% A95P + K304D + A95P + K304D + Q380L + I297L + Q380L + I297L + E368P + T107A E368P + T107A + A286T

II. Immobilizing the Transaminase Mutant of the Application

2.1 Preparation of Transaminase Cross-Linked Enzyme Aggregates (CLEAs)

In the application, transaminases of female parent R416T+T7C+S47C mutant, single point mutants and combined mutants screened on the basis of female parent mutant were immobilized by cross-linking method to prepare transaminase cross-linked enzyme aggregates.

In general, the preparation of the cross-linked enzyme aggregates is mainly carried out in two steps: (1) forming an enzyme protein aggregation precipitate; (2) cross-linking between precipitates.

The enzyme protein can be coagulated and precipitated by a salt fractionation, an isoelectric precipitation method, a heavy metal salt precipitation method or an organic solvent precipitation method to obtain enzyme protein aggregates. Typically, the enzymatic protein precipitate is a reversible precipitate that can be re-dissolved in aqueous solution.

And after protein precipitation, adding a cross-linking agent to further connect protein precipitates through covalent bonds to form water-insoluble precipitate-cross-linked enzyme aggregates. The cross-linking agent used is a bifunctional or multifunctional reagent, the bifunctional reagent comprises glutaraldehyde, N, N-methylene bisacrylamide (MBA), bismaleimide and the like, and the multifunctional reagent dextran (molecular weight is 6 KDa-200 KDa). Free amino group, phenol group, imidazole group and sulfhydryl group of enzyme protein can participate in cross-linking reaction.

The buffer for preparing the immobilized enzyme solution contains PLP of 0.4-1 mg/mL, and the pH value of the enzyme solution is 7.0-8.0. The precipitant used for preparing the enzyme protein precipitate is ethanol, isopropanol and/or ammonium sulfate, and the final concentration of the precipitant is 90%. The cross-linking agent used to prepare the cross-linked aggregates of the enzyme proteins was a 25% glutaraldehyde solution with a final glutaraldehyde concentration of 200 mM-500 mM.

The prepared cross-linked enzyme aggregate can be directly subjected to catalytic reaction in an aqueous phase with the aqueous cross-linked enzyme obtained by filtration, or the aqueous cross-linked enzyme can be lyophilized to obtain a dry powder and then applied. The lyophilized powder may also be applied to the reaction in the organic solvent phase. After the cross-linked enzyme aggregate is used once, the cross-linked enzyme aggregate can be recovered by centrifuging or filtering and the like and then used again, the repeated use times are counted in the range that the activity loss is less than 5% compared with the first use, the cross-linked enzyme aggregate is used in an aqueous phase. Compared with the free enzyme, the activity recovery is more than 80%, and the female parent R416T+T7C+S47C can be reused for 3 times, the reuse times of single point mutants and/or combined mutants on the basis of female parent were significantly higher than those of female parents, and the reuse times of the best mutants were up to 13 times.

The cross-linked enzymes of some mutants can be reused at least 6 times in a system containing 35% methanol. The stability of free enzyme activity of the mutant was improved, and the enzyme activity recovery and reuse times were also increased after immobilization.

The emulsification phenomenon was obviously reduced with cross-linked enzyme to catalyze the reaction and extracting the product from the aqueous phase with organic solvent after the reaction. The preparation of cross-linked enzyme has the advantages of no carrier, low cost, catalyzing reaction with cross-linked enzyme, more times of repeated use, comprehensive use times, reduced amount of enzyme and lower cost than free enzyme. The cross-linked enzyme lyophilized powder is reacted in 100% organic phase solvent, and when the female parent is repeatedly used for the second time, the activity is lost by more than 10% compared with that for the first time. However, some mutants could be reused up to 5 times with less than 5% loss of activity compared to the first time.

2.2 Embedded-Crosslinked Immobilization Method of Transaminase

CLEAs have no carrier support, small immobilized enzyme particles (<10 pin) and poor mechanical strength, the enzyme is easy to harden in the process of filtering and recovering the enzyme, and the enzyme cannot be well dispersed in the reaction system in the next use.

In order to solve the problem, glutaraldehyde can be used as a cross-linking agent in combination with two technologies of cross-linking and embedding, glutaraldehyde is added dropwise to a mixed solution containing enzyme liquid, acrylamide and methylene diacrylamide to enable the glutaraldehyde and free enzyme to form Schiff base to prepare a cross-linked enzyme aggregate, an initiator ammonium persulfate is added to form polyacrylamide gel, and the cross-linked enzyme aggregate is embedded into a polyacrylamide gel matrix to obtain stable immobilized enzyme.

In the application, transaminases of female parent R416T+T7C+S47C mutant, single point mutants and combined mutants screened on the basis of female parent mutant were immobilized by embedded-crosslinked method to prepare embedded-crosslinked enzyme.

The prepared embedded-crosslinked enzyme, whose enzyme activity recovery is more than 80%, after the aqueous phase reaction is used once, it can be easily recovered by filtering and the like and then used again, the repeated use times are counted in the range that the activity loss is less than 5% compared with the first use, the female parent R416T+T7C+S47C can be reused for 8 times, the reuse times of single point mutants and/or combined mutants on the basis of female parents were significantly higher than those of female parents, and the reuse times of the best mutants were up to 18 times.

The embedded-crosslinked enzymes of some mutants can be reused at least 12 times in a system containing 35% methanol. Extracting the product from the aqueous phase with organic solvent after the reaction, the emulsification phenomenon was obviously reduced.

2.3 Adsorption Immobilization Method of Transaminase

The adsorbed immobilized enzyme can be prepared by the adsorption and combination of enzyme molecule and water-insoluble carrier by means of electrostatic interaction, hydrogen bond, hydrophobic interaction and so on. The method has mild conditions and is not easy to cause denaturation of the enzyme, but the enzyme is easily separated from the carrier in aqueous solution and cannot be recycled, so the immobilized enzyme prepared by adsorption method is mainly used in the reaction in organic solvents.

The carriers that can be used to adsorbed immobilized enzymes can be divided into two types: inorganic carriers and macromolecular carrier. Inorganic carriers include activated carbon, porous glass, emathlite, bleaching clay, kaolinite, alumina, silica gel, bentonite, hydroxyapatite, calcium phosphate, metal oxides and the like; macromolecular carriers include starch, glutelin, macroporous synthetic resins, ceramics, etc.

The carrier used in the application is a macroporous synthetic resin carrier, comprising a matrix and an optional functional group that modify the matrix, wherein the matrix includes, but is not limited to, polystyrene resin, polymethacrylate resin or styrene-methacrylate copolymer. In addition, various types of carriers can be modified with octadecyl functional group. Table 9 below is listed as the carrier suitable for the adsorption and immobilization of transaminase in the application.

TABLE 9 Adsorption type carrier Carrier Name Matrix Functional Group Diaion Polymethacrylate No X17S0401 Polymethacrylate No ECR8806 Polymethacrylate No EXE120 Polymethacrylate Octadecyl ECR-1030 Polymethacrylate No ECR-1090 polystyrene No

In this application, the transaminase and the macroporous resin carrier are directly combined in physical modes such as hydrophobic bonds, hydrogen bonds and the like.

Transaminases of female parent R416T+T7C+S47C mutant, single point mutants and combined mutants screened on the basis of female parent mutant were immobilized by physical adsorption binding method.

The buffer used for preparing the enzyme solution contains 0.4-1 mg/mL of PLP, the pH of the buffer is 7.0-8.0, and the buffer salt is Na₂HPO₄—NaH₂PO₄, Tris-Cl or boric acid-sodium hydroxide.

The prepared adsorption immobilized enzyme can be dried by nitrogen blow drying, vacuum drying, freeze drying and so on.

In this application, the transaminase is bound to the carrier by adsorption, and the activity recovery is more than 80%; reacting in organic solvent, the immobilized enzyme is recovered by filtration or liquid suction by syringe, which can be reused. Compared with the first use, the number of repeated uses was counted in the range of activity loss less than 5%. For some mutant immobilized enzymes, the immobilized enzyme could be reused for 6 times, and the activity loss was less than 5%.

2.4 Covalent Immobilization Method of Transaminase

Covalent immobilization of an enzyme is that a non-essential group of an enzyme protein is irreversibly linked with a water-insoluble carrier through a covalent bond, and protein groups capable of being coupled under mild conditions comprise: amino, carboxyl, sulfhydryl of cysteine, imidazolyl of histidine, phenolic group of tyrosine, hydroxyl of serine and threonine. The group covalently bound with the carrier is usually not the group necessary for the enzyme to express activity.

2.4.1 Covalent Immobilized Enzyme Carrier

The immobilized enzyme carrier can be inorganic materials such as silica, glass, minerals, celite and the like; natural organic materials such as carboxymethyl cellulose, dextran, agarose, pectin, chitosan and the like; and non-natural organic synthetic polymers such as polystyrene resins, polymethacrylate resins or copolymers of styrene and methacrylate. These carriers may be further functionalized to facilitate binding to the protein molecule, such as by incorporating amino, hydroxyl, epoxy, octadecyl and other functional groups on the carrier. The amino-functional carrier and the hydroxyl-functional carrier can bind to enzyme protein molecule through ionic bonds, the amino-type carrier can also covalently bind to the enzyme protein, the epoxy-functional carrier mainly binds to the enzyme protein through covalent bonds, and the octadecyl-functional carrier binds to the enzyme molecule through hydrophobic interaction. The carrier may take any shape or form, such as a film, tube, sheet, bead, particle, chip, optical fiber, etc.

The carrier used in the present application is chitosan, resin and porous glass.

Chitosan can be used as a carrier for enzyme immobilization because of its good biocompatibility, high shape plasticity (which can be made into gel, film, fiber and other shapes), non-toxicity, easy chemical modification and other characteristics (ProcessBiochem, 2005; 40: 2833-40). Chitosan itself is soluble in water and needs to be prepared into water-insoluble carrier particles by solvent evaporation, emulsification, coacervation and other methods (MacromolBiosci, 2003; 3: 511-20). The carrier particles produced by emulsification are small and uniform and are generally preferred. The chitosan molecules have active hydroxyl groups, amino groups and the like, the enzyme can be adsorbed and bound through ionic bonds, hydrogen bonds, Van der Waals force and others, but the adsorption effect is weak, the enzyme is easy to fall off, and the common cross-linking agents such as formaldehyde, glutaraldehyde and the like are activated and then covalently bound to the enzyme.

The resin carrier used in the application comprises a matrix and functional groups that modify the matrix, wherein the matrix includes, but is not limited to, polystyrene resins, polymethacrylate resins and copolymers of styrene-methacrylate. Suitable functional groups carried by such matrixs include, but are not limited to, short-chain amino groups, long-chain amino groups and epoxy groups. Table 10 below is listed as the carrier suitable for the immobilization of transaminase in the application.

TABLE 10 Carrier Name Matrix Functional Group ECR8309 Polymethacrylate Short-chain amino group (C2) ECR8409 Polymethacrylate Long-chain amino group (C6) ECR8285 Polymethacrylate Epoxy-group

In the application, the transaminase is directly bound to the resin with epoxy functional group through covalent bond, and to the resin with amino functional group activated by glutaraldehyde through covalent bond.

2.4.2 Method of Covalent Immobilization

In the application, transaminases of female parent R416T+T7C+S47C mutant, single point mutants and combined mutants screened on the basis of female parent mutant were immobilized by covalent binding method.

The buffer solution used for preparing the enzyme solution contains 0.4-1 mg/mL of PLP, the pH of the buffer solution is 7.0-8.0, and the buffer salt is Na₂HPO₄—NaH₂PO₄, Tris-Cl or boric acid-sodium hydroxide. The molecular weight of chitosan used in the present application includes, but is not limited to, 300-500 KDa, a carrier is prepared by an emulsification method, after activating the carrier with glutaraldehyde, adding enzyme solution, incubating for 6 h at 20° C., collecting the precipitate by filtration or centrifugation, and rinsing the precipitate with buffer.

Covalently immobilized to the amino-type carrier, first activating the carrier with glutaraldehyde, then adding enzyme solution, incubating overnight at 20° C., collecting the precipitate by filtration, and rinsing the precipitate with buffer. Covalently immobilized to epoxy-based carrier, directly mixing enzyme solution with the carrier, incubating overnight at 20° C., then standing for 20 h, collecting the precipitate by filtration, and rinsing the precipitate with buffer.

The prepared immobilized enzyme can be dried by nitrogen blow drying, vacuum drying, freeze drying and so on.

In the application, the transaminase is immobilized to the above carriers by covalent binding, and immobilized to a chitosan carrier, and the activity recovery is 50%-60%; immobilized to a short-chain amino carrier, the activity recovery is 50%-70%; immobilized to a long-chain amino-type carrier, the activity recovery is 70%-80%; immobilized to an epoxy-based carrier, the activity recovery is 40%-60%. The activity of the immobilized enzyme of the mutant is obviously improved compared with that of the female parent immobilized enzyme. The immobilized enzyme is recovered by filtration or liquid suction by syringe, which can be reused. Compared with the first use, the number of repeated uses was counted in the range of activity loss less than 5%, for enzyme immobilized to the chitosan carrier, the immobilized enzyme could be reused for 3 times, and the activity loss was less than 5%. Immobilized to a short-chain amino-type carrier, some enzymes can be reused for 5 times; Immobilized to a long-chain amino-type carrier, the enzyme of some mutants could be reused for 11 times; Immobilized to epoxy-based carrier, some enzymes can be reused for 6 times. The reusable times of mutant immobilized enzyme was significantly higher than that of female parent immobilized enzyme. Some transaminases after covalent immobilization can play catalytic role in 100% organic solvent, some mutants can react in organic solvent after immobilization, and the activity loss is less than 5% after repeated use for 3 times. Playing a catalytic role in 35% methanol solution, some mutants were reused 5 times after immobilization, and the activity loss was less than 5%.

2.5 Metal Ion Chelating Immobilization Method

Porous glass is very suitable for enzyme immobilization because of its inert material and good water permeability. The silanol groups on the glass and channel surface thereof are used as binding sites to bind to the enzyme and achieve immobilization, but the silanol group on the surface of traditional glass has limited density and uneven distribution, high binding steric hindrance to the enzyme, low protein loading (Science, 2010, 329, 305-309; JChromatogr, 1976, 125, 115-127) and easy to inactivate the enzyme. Covering the inner and outer surface of porous glass with a layer of organic polymer film can form a more favorable environment for enzyme immobilization. (Langmuir, 2004, 20, 10639-10647). The polymer film may be further modified as desired to add various functional groups suitable for immobilization to the surface.

The histidine-tagged protein can be purified by solid-phase metal affinity chromatography, histidine residues in the protein can be chelated with metal ions (Ni²⁺, Co²⁺, Fe³⁺) chelated on a water-insoluble matrix, and then the target protein can be eluted with an imidazole-containing buffer (Nature, 1975, 258, 598-599). Based on this technology, the histidine-tagged enzyme can be specifically chelated with the carrier with metal ions chelated at the end, and the purpose of immobilization can be achieved. At the same time, the specificity of the method is high, and miscellaneous proteins can hardly be immobilized.

The glass carrier used in the application is coated on the inner and outer surface of porous glass by polymer film, and the polymer film may be hydrophilic polymer such as acrylic polymer, semi-hydrophilic styrene and acrylonitrile polymer and hydrophobic polymer such as chloromethyl styrene polymer. The surface of the film is modified by amino and then acylated by 2, 4-dihydroxyacetophenone, and the hydroxyl of the 2, 4-dihydroxyacetophenone is chelated with metal ions, so that one end of the 2, 4-dihydroxyacetophenone is bound to the carrier and the other end of the 2, 4-dihydroxyacetophenone is chelated with the metal ions through the arm action of the 2, 4-dihydroxyacetophenone, so that the end of the glass carrier is provided with the metal ions and can be affinity bound to the histidine-tagged protein to achieve specific immobilization. (ChemicalCommunications, 2014, 50 (65): 9134-7). Chelated metal ions include, but are not limited to, Ni²⁺, Co²⁺ and Fe³⁺. Table 11 below is listed as the carrier suitable for the immobilization of transaminase in the application.

TABLE 11 Carrier Name Property Metal-ion EziG-101 Hydrophilic Fe³⁺ EziG-102 Semi-hydrophilic Fe³⁺ EziG-103 Hydrophobic Fe³⁺

In the application, transaminases of female parent R416T+T7C+S47C mutant, single point mutants and combined mutants screened on the basis of female parent mutant were immobilized by covalent binding method.

The buffer solution used for preparing the enzyme solution contains 0.4-1 mg/mL of PLP, the pH of the buffer solution is 7.0-8.0, and the buffer salt is Na₂HPO₄—NaH₂PO₄, Tris-Cl or boric acid-sodium hydroxide.

Covalently immobilized to the porous glass carrier, directly mixing the enzyme solution with carrier, incubating for 40-60 min at 20° C., collecting the precipitate by filtration, and rinsing the precipitate with the buffer.

The prepared immobilized enzyme can be dried by nitrogen blow drying, vacuum drying, freeze drying and so on.

In this application, the transaminase is bound to the carrier by chelation, and the activity recovery is 70%-80%. The immobilized enzyme is recovered by filtration or liquid suction by syringe, which can be reused. Reacting in an aqueous solvent, compared with the first use, the number of reuse times was counted in the range of activity loss less than 5%. For some mutant immobilized enzymes, the immobilized enzyme could be reused for 12 times, and the activity loss was less than 5%; Reacting in organic solvents, compared with the first use, the number of reuse times was counted in the range of activity loss less than 5%. For some mutant immobilized enzymes, the immobilized enzyme could be reused for 8 times.

III. Application Method of Immobilized Transaminase

The immobilized transaminase of the present application can transform the amino acceptors shown in substrate 1 and substrate 2 into the corresponding primary amines, and the amino donor used is isopropylamine.

The immobilized transaminase of the application can be applied in the following solvents: 100% aqueous solution, solvent containing 20%-50% DMSO, solvent containing 35% methanol, or 100% water saturated organic solvent (e.g., may be 100% water saturated methyl tert-butyl ether or 100% water saturated isopropyl acetate).

The immobilized enzyme disclosed by the invention can be applied to batch reactions in a stirring mode, and can also be applied to continuous flow reactions filled in a pipeline reactor.

The batch stirring reaction operation mode is as follows: adding the raw materials, namely the amino acceptor, the amino donor, the immobilized enzyme, the coenzyme PLP and the solvent into the reaction vessel at one time, and reacting for more than 16 h by means of mechanical stirring. After the reaction, the immobilized enzyme was recovered by filtration and applied to the next round of reaction.

The operation mode of the continuous reaction is as follows: filling the immobilized enzyme into a tubular reactor, completely dissolving raw materials, namely an amino acceptor, an amino donor and coenzyme PLP, into a reaction solution with a proper solvent, injecting the reaction solution into the tubular reactor filled with the immobilized enzyme at a proper flow rate with a plunger pump, and receiving a product solution with the solvent at an outlet.

During continuous reaction operation, the solvent can be 35% methanol solution or 100% water-saturated methyl tertiary ether.

The benefits of the present application are further illustrated by the following specific examples.

Example 1: Mutant Tolerance Test at 30° C., pH 9.5 and 50% DMSO

Crude enzyme was treated for 1 h at 30° C., pH 9.5, DMSO concentration of 50%, then 0.1 g substrate 1, 4 eq isopropylamine hydrochloride and 0.6-1 mg PLP (pyridoxal 5′-phosphate) were added to a 10 mL reaction flask, then 5 mg of the treated enzyme was added and thermostatically stirred for 16 h in the environment of 30° C., pH 9.5, DMSO concentration of 50%. The transformation rate was measured by HPLC and the mutant reaction data are shown in Table 12 below.

TABLE 12 Transformation Transformation Transformation Mutation site rate (%) Mutation site rate (%) Mutation site rate (%) Female parent 67.7 K51R 77.5 T107F 92.3 R416T + T7C + S47C M356L 80.4 A95P 88.6 T107A 94.4 F364L 80.4 E368P 97.1 G110P 89.2 C404L 78.7 Q346E 92.6 Q380L 95.5 M430L 76.5 H333K 87.9 K193I 93.5 R405E 95.4 D371G 83.2 I297L 96.4 R405A 85.7 E246A 87.2 R305H 97.1 K90G 73.2 C328A 93.8 F111Y 78.6 K219T 73.9 N412G 80.5 K190E 88.7 K69N 83.9 G201C 86.7 G201C 86.7 K304D 90.9 T402P 84.3 A286T 98.2

Example 2: Mutant Tolerance Test at 45° C., pH 10 and 50% DMSO

Crude enzyme was treated for 1 h at 45° C., pH 10, DMSO concentration of 50%, then 0.1 g substrate 1, 4 eq isopropylamine hydrochloride and 0.6-1 mg PLP (pyridoxal 5′-phosphate) were added to a 10 mL reaction flask, then 5 mg of the treated enzyme was added and thermostatically stirred for 16 h in the environment of 45° C., pH 10, DMSO concentration of 50%. The transformation rate was measured by HPLC and the mutant reaction data are shown in Table 13 below.

TABLE 13 Transfor- Transfor- mation mation Mutation site rate (%) Mutation site rate (%) Female parent 13.7 R405E + A95P + 90.7 R416T + T7C + K304D + Q380L S47C R405E 64.3 R405E + K90G + 94 A95P + K304D + Q380L A95P 66.7 R405E + K90G + 97.3 A95P + K304D + Q380L + I297 Q380L 83.5 R405E + K90G + 97.4 A95P + K304D + Q380L + E368P I297L 87.3 R405E + K90G + 89.3 A95P + K304D + Q380L + Q346E F111Y 46.3 R405E + K90G + 90.8 A95P + K304D + Q380L + H333K R305H 37.6 R405E + K90G + 64.1 A95P + K304D + Q380L + D371G K190E 39.8 R405E + K90G + 59.4 A95P + K304D + Q380L + C328A K51R + W187Y 83.1 R405E + K90G + 57.9 A95P + K304D + Q380L + T402P R405E + A95P + 92.1 R405E + K90G + 92.2 K304D A95P + K304D + Q380L + T107A K69N 30.7 G201C 28.9 A286T 92.5 −/− −/−

Example 3: Mutant Tolerance Test at 30° C., pH 8 and 35% Methanol

Crude enzyme was treated for 1 h at 30° C., pH 8, MeOH concentration of 35%, then 0.1 g substrate 1, 4 eq isopropylamine hydrochloride and 0.6-1 mg PLP (pyridoxal 5′-phosphate) were added into a 10 mL reaction flask, then 5 mg of the treated enzyme was added and continued to thermostatically stir for 16 h in the environment of 30° C., pH 8, MeOH concentration of 35%. The transformation rate was measured by HPLC and the mutant reaction data are shown in Table 14 below.

TABLE 14 Transfor- Transfor- mation mation Mutation site rate Mutation site rate (%) Female parent 8.9 R405E + K90G + 58.5 R416T + T7C + A95P + K304D + S47C Q380L Q380L 66.7 R405E + K90G + 91.2 A95P + K304D + Q380L + E368P I297L 60.2 R405E + K90G + 77.7 A95P + K304D + Q380L + Q346E F111Y 28.6 R405E + K90G + 78.2 A95P + K304D + Q380L + H333K R305H 53.1 R405E + K90G + 78.6 A95P + K304D + Q380L + C328A K190E 44.8 R405E + K90G + 83.4 A95P + K304D + Q380L + T107A K193I 60.4 R405E + K90G + 97 A95P + K304D + Q380L + I297L R405E + A95P + 86 A95P + R405E + 96 K304D K304D + Q380L + K90G + I297L + E368P + T107A K69N 34.5 G201C 35.1 A286T 64.3 R405E + K90G + 70.9 A95P + K304D + Q380L + I297L + E368P + T107A + A286T R405E + K90G + 61.9 R405E + K90G + 64.3 A95P + K304D + A95P + K304D + Q380L + I297L + Q380L + I297L + E368P + T107A + E368P + T107A + K69N G201C R405E + K90G + 40.4 R405E + K90G + 34.5 A95P + K304D + A95P + K304D + Q380L + N412G Q380L + T402P R405E + K90G + 27.8 −/− −/− A95P + K304D + Q380L + D371G

Example 4: Mutant Tolerance Test at 45° C., pH 8 and 40% Methanol

Crude enzyme was treated for 1 h at 45° C., pH 8, MeOH concentration of 40%, then 0.1 g substrate 1, 4 eq isopropylamine hydrochloride and 0.6-1 mg PLP (pyridoxal 5′-phosphate) were added into a 10 mL reaction flask, then 5 mg of the treated enzyme was added and continued to thermostatically stir for 16 h in the environment of 45° C., pH 8, MeOH concentration of 40%. The transformation rate was measured by HPLC and the mutant reaction data are shown in Table 15 below.

TABLE 15 Transfor- Transfor- mation mation Mutation site rate (%) Mutation site rate (%) Female parent  2.9 R405E + K90G + 96.5% R416T + T7C + A95P + K304D + S47C Q380L + I297L + A286T R405E + K90G + 98.2% R405E + K90G +  98% A95P + K304D + A95P + K304D + Q380L + I297 Q380L + I297L + E368P R405E + K90G + 86.7 R405E + K90G + 87.8 A95P + K304D + A95P + K304D + Q380L + I297L + Q380L + I297L + E368P + T107A + E368P + T107A + K69N G201C R405E + K90G +  96% R405E + K90G + 89.8 A95P + K304D + A95P + K304D + Q380L + I297L + Q380L + I297L + E368P + T107A E368P + T107A + A286T

Example 5: Cross-Linking Immobilization

0.1 g enzyme powder was dissolved in 2 mL of phosphate buffer (0.1 M PB, pH 7.0-8.0, containing 0.4-1 mg/mL PLP (pyridoxal 5′-phosphate)), 18 mL ethanol, or 18 mL isopropanol, or ammonium sulfate (final saturation of 90%) was slowly added as a precipitant with stirring in an ice-water bath, and after 10 min of stirring, 1.1-2.7 mL 25% glutaraldehyde solution (final concentration of 200-500 mM) was added, centrifuged or filtered after stirring in the ice-water bath for 30-40 min, the precipitate was washed with a phosphate buffer for three times, stored at 4° C., and directly applied to an aqueous phase reaction. Or the cross-linked enzyme aggregate is lyophilized, and the cross-linked enzyme aggregate lyophilized powder after lyophilization can be applied in aqueous phase and organic phase reactions.

Example 6: Reaction of Cross-Linked Enzyme Aggregates in Aqueous Phase for Testing Activity

To a 10 mL reaction flask, 0.3 mL DMSO was added, 0.1 g substrate 1 was dissolved, 4 eq isopropylamine hydrochloride and 1.0 mg PLP (pyridoxal 5′-phosphate) were added, 0.1 M PB 7.0 was added until the final volume of the reaction solution was 1 mL, and 5 mg enzyme or cross-linked enzyme aggregate wet enzyme prepared from 5 mg enzyme or cross-linked enzyme aggregate lyophilized powder was added and stirred at 45° C. for 16 h. The transformation rate was measured by HPLC and reaction data are shown in Table 16 below.

TABLE 16 Reuse Transfor- times with Immobilization mation activity Strain number form rate (%) loss <5% Female parent No 98.20% 1 R416T + T7C + Cross-linked enzyme 92.30% 3 S47C wet enzyme Cross-linked enzyme 86.20% 1 lyophilized powder A95P No 97.80% 1 Cross-linked 98.20% 6 wet enzyme Cross-linked enzyme 92.70% 5 lyophilized powder R405E + K90G + No 98.60% 1 A95P + K304D + Cross-linked 97.90% 10 wet enzyme Q380L Cross-linked enzyme 97.30% 8 lyophilized powder R405E + K90G + No 98.50% 1 A95P + K304D + Cross-linked 98.30% 14 wet enzyme Q380L + I297L Cross-linked enzyme 98.50% 13 lyophilized powder R405E + K90G + Cross-linked 98.30% 13 A95P + K304D + wet enzyme Q380L + I297L + E368P + T107A R405E + K90G + Cross-linked 98.50% 14 A95P + K304D + wet enzyme Q380L + I297L + E368P + T107A + A286T R405E + K90G + Cross-linked 98.00% 12 A95P + K304D + wet enzyme Q380L + I297L + E368P + T107A + K69N R405E + K90G + Cross-linked 98.30% 12 A95P + K304D + wet enzyme Q380L + H333K R405E + K90G + Cross-linked 98.40% 11 A95P + K304D + wet enzyme Q380L + E368P K51R + W187Y Cross-linked 98.20% 9 wet enzyme R405E + K90G + Cross-linked 98.50% 10 A95P + K304D + wet enzyme Q380L + Q346E R405E + K90G + Cross-linked 98.40% 10 A95P + K304D + wet enzyme Q380L + C328A

Example 7: Reaction of Cross-Linked Enzyme in Organic Phase for Testing Activity

To a 10 mL reaction flask, 1 mL water-saturated methyl tert-butyl ether was added, followed by 10 mg substrate 1 and 4 eq isopropylamine, then cross-linked enzyme aggregates lyophilized powder prepared from 10 mg enzyme powder was added, and stirred for 16 h at 30° C. The transformation rate was measured by HPLC and reaction data are shown in Table 17 below.

TABLE 17 Reuse Transfor- times with Immobilization mation activity Strain number form rate (%) loss <5% Female parent Cross-linked enzyme 87.90% 1 R416T + T7C + lyophilized powder S47C A95P Cross-linked enzyme 90.30% 3 lyophilized powder R405E + K90G + Cross-linked enzyme 90.60% 3 A95P + K304D + lyophilized powder Q380L R405E + K90G + Cross-linked enzyme 94.70% 5 A95P + K304D + lyophilized powder Q380L + I297L R405E + K90G + Cross-linked enzyme 92.10% 5 A95P + K304D + lyophilized powder Q380L + I297L + E368P + T107A R405E + K90G + Cross-linked enzyme 90.90% 4 A95P + K304D + lyophilized powder Q380L + I297L + E368P + T107A + A286T

Example 8: Reaction of Transaminase Embedded-Crosslinked Immobilized Enzyme in Aqueous Phase for Testing Activity

To a 10 mL reaction flask, 0.4 mL DMSO was added (final concentration of DMSO being 40%), 0.1 g substrate 1 was dissolved, 4 eq isopropylamine hydrochloride and 1.0 mg PLP (pyridoxal 5′-phosphate) were added, 0.1 M PB 7.0 was added until the final volume of the reaction solution was 1 mL, and 5 mg enzyme or embedded-crosslinked immobilized enzyme prepared from 5 mg enzyme was added and stirred at 45° C. for 16 h. The transformation rate was measured by HPLC and reaction data are shown in Table 18 below.

TABLE 18 Reuse Transfor- times with Immobilization mation activity Mutation site form rate (%) loss <5% Female parent No 93.9 1 R416T + T7C + Embedded- 54.9 8 S47C crosslinked immobilized enzyme R405E + K90G + No 97.8 1 A95P + K304D + Covalent 76.4 11 Q380L immobilized enzyme R405E + K90G + No 98.1 1 A95P + K304D + Embedded- 98.0 11 Q380L + I297L + crosslinked E368P + T107A immobilized enzyme R405E + K90G + No 97.5 1 A95P + K304D + Embedded- 98.0 10 Q380L + Q346E crosslinked immobilized enzyme R405E + K90G + No 97.9 1 A95P + K304D + Covalent 97.6 18 Q380L + I297L immobilized enzyme

Example 9: Reaction of Transaminase Embedded-Crosslinked Immobilized Enzyme in 35% Methanol Water Solution for Testing Activity

In a 10 mL reaction flask, 0.35 mL methanol (methanol final concentration being 40%) was added, 0.1 g substrate 1 was dissolved, 4 eq isopropylamine hydrochloride and 1.0 mg PLP (pyridoxal 5′-phosphate) were added, 0.1 M PB 7.0 was added until the final volume of the reaction solution was 1 mL, and 10 mg enzyme or embedded-crosslinked immobilized enzyme prepared from 10 mg enzyme was added and stirred at 30° C. for 16 h. The transformation rate was measured by HPLC and reaction data are shown in Table 19 below.

TABLE 19 Reuse Transfor- times with Immobilization mation activity Mutation site form rate (%) loss <5% Female parent No 60.6 1 R416T + T7C + Embedded- 54.9 6 S47C crosslinked immobilized enzyme R405E + K90G + No 98.3 1 A95P + K304D + Covalent 76.4 9 Q380L immobilized enzyme R405E + K90G + No 98.5 1 A95P + K304D + Covalent 97.6 12 Q380L + I297L immobilized enzyme

Example 10: Adsorption Immobilization Method of Transaminase

4 mL PB buffer containing 0.4 mg/mL PLP (100 mM pH 7.0) was added into the carrier, and 0.1 g enzyme was added at the same time, stirred in a low speed of 80 rpm overnight at 20° C. The supernatant was removed, the precipitate was washed 3-4 times with buffer, the supernatant was removed, the precipitate was blown dry with nitrogen, or dried by freeze drying and stored at 4° C.

Example 11: Reaction of Transaminase Adsorptive Immobilized Enzyme in Organic Phase for Testing Activity

In a 10 mL reaction flask, 1 mL water-saturated methyl tert-butyl ether was added, followed by 10 mg substrate 1 and 4 eq isopropylamine, then immobilized transaminase prepared from 20 mg enzyme was added, and stirred for 16 h at 30° C. The transformation rate was measured by HPLC and reaction data are shown in Table 20 below.

TABLE 20 Reuse Transfor- times with Immobilization mation activity Mutation site form Carrier rate (%) loss <5% Female parent Adsorption Diaion 64.3 2 R416T + T7C + immobilized HP2MG S47C enzyme X17S0401 57.2 2 EXE120 53.9 2 ECR8806 60.2 3 ECR1030 49.2 2 ECR1090 43.8 1 R405E + K90G + Adsorption Diaion 91.4 4 A95P + K304D + immobilized HP2MG Q380L + I297L enzyme X17S0401 89.2 4 EXE120 90.7 4 ECR8806 94.8 6 ECR1030 79.9 3 ECR1090 72.4 3 R405E + K90G + Adsorption ECR8806 92.4 4 A95P + K304D + immobilized Q380L + H333K enzyme R405E + K90G + Adsorption ECR8806 94.7 4 A95P + K304D + immobilized Q380L + Q346E enzyme R405E + K90G + Adsorption ECR8806 82.8 3 A95P + K304D + immobilized Q380L + N412G enzyme R405E + K90G + Adsorption ECR8806 96.8 6 A95P + K304D + immobilized Q380L + I297L + enzyme E368P + T107A R405E + K90G + Adsorption ECR8806 76.3 5 A95P + K304D + immobilized Q380L + I297L + enzyme E368P + T107A + A286T R405E + K90G + Adsorption ECR8806 81.5 5 A95P + K304D + immobilized Q380L + I297L + enzyme E368P + T107A + G201C

Example 12: Immobilization of Transaminase with Chitosan as Carrier

Preparation of chitosan carrier: 5 g chitosan (molecular weight 300 KDa-500 KDa) was added to 250 mL 1% acetic acid solution and dissolved by heating in microwave oven to prepare aqueous phase. The oil phase was prepared by evenly mixing 300 mL toluene with 2.2 g Span 80, 1.2 mL n-hexanol and stirring at room temperature for 2 h. An aqueous phase was slowly dropwise adding into an oil phase under stirring to prepare an emulsion, the emulsion was poured into a 1.5 L 12% NaOH solution, stirred for 3 h, 1 L ethanol was added, filtered, a filter cake was thoroughly cleaned with purified water to obtain about 40 g wet carrier, the wet carrier is soaked in 140 mL pure water, and stored at 4° C.

Activating a carrier: 1.1 mL 25% glutaraldehyde (final glutaraldehyde concentration of 2.5%) was added per milliliter of wet carrier.

Immobilization: 0.2 g enzyme was added into the activated carrier, stirred for 6 h at 20-25° C., the carrier was washed, centrifuged to remove the supernatant, and the precipitate is the immobilized enzyme, and storing at 4° C.

Example 13: Immobilization of Transaminase on C6 Amino Carrier

Activating a carrier: 1 g carrier ECR8409 was washed 1-2 times with 20 mM low ionic strength buffer, the supernatant was removed, 4 mL 2% glutaraldehyde (prepared from 20 mM low ionic strength buffer dilution reagent and 25% glutaraldehyde), at 20° C., activated at 80 rpm for 1 h, washed 1-2 times with 20 mM buffer, and the supernatant was removed.

Immobilization: 4 mL PB buffer containing 0.4 mg/mL PLP (20 mM pH 7.0) was added into the activated carrier, and 0.1-0.2 g enzyme was added at the same time, stirred in a low speed of 80 rpm overnight at 20° C. The supernatant was removed, the precipitate was washed 3-4 times with buffer, the supernatant was removed, and the precipitate was blown dry with nitrogen, or dried by freeze drying and stored at 4° C.

Example 14: Immobilization of Transaminase on Epoxy Carrier

1 g carrier ECR8285 was washed 1-2 times with 100 mM PB buffer, the clear liquid was removed, 4 mL Buffer (100 mM PB, pH 7.0, containing 1 M NaCl) was added, 0.1 g-0.2 g enzyme was added at the same time, at 20° C., stirred at low speed of 80 rpm overnight (18-20 h), and then stood at 4° C. for 20 h. The supernatant was removed and the precipitate was washed 3-4 times with Buffer, blown dry with nitrogen and stored for 4° C.

Example 15: Reaction of Covalent Immobilized Transaminase in Aqueous Phase for Testing Activity

In a 10 mL reaction flask, 04 mL DMSO (DMSO final concentration being 40%) was added, 0.1 g substrate 1 was dissolved, 4 eq isopropylamine hydrochloride and 1.0 mg PLP (pyridoxal 5′-phosphate) were added, 0.1 M PB7.0 was added until the final volume of the reaction solution was 1 mL, and 5 mg enzyme or immobilized transaminase prepared from 5 mg enzyme was added and stirred at 45° C. for 16 h. The transformation rate was measured by HPLC and reaction data are shown in Table 21 below.

TABLE 21 Reuse Transfor- times with Immobilization mation activity Mutation site form Carrier rate (%) loss <5% Female parent No No 60.6 1 R416T + T7C + Covalent Chitosan 36.1 3 S47C immobilized ECR8309 32.8 2 enzyme ECR8409 41.5 3 ECR8285 31.7 2 A95P No No 97.8 1 Covalent Chitosan 65.2 3 immobilized ECR8309 63.7 5 enzyme ECR8409 78.4 6 ECR8285 57.2 4 R405E + K90G + No No 98.3 1 A95P + K304D + Covalent Chitosan 76.4 4 Q380L immobilized ECR8309 72.1 5 enzyme ECR8409 88.6 11 ECR8285 69.2 6 R405E + K90G + No No 98.5 1 A95P + K304D + Covalent ECR8409 97.6 12 Q380L + I297L immobilized enzyme Q380L No No 97.8 1 Covalent ECR8409 87.6 7 immobilized enzyme R405E No No 97.1 1 Covalent ECR8409 89.5 6 immobilized enzyme K51R + W187Y No No 96.8 1 Covalent ECR8409 83.3 6 immobilized enzyme R405E + A95P + No No 97.6 1 K304D Covalent ECR8409 88.9 8 immobilized enzyme R405E + K90G + No No 98.1 1 A95P + K304D + Covalent ECR8409 90.3 11 Q380L + E368P immobilized enzyme

Example 16: Reaction of Covalent Immobilized Transaminase in 35% Methanol Water Solution for Testing Activity

In a 10 mL reaction flask, 0.35 mL methanol (methanol final concentration being 40%) was added, 0.1 g substrate 1 was dissolved, 4 eq isopropylamine hydrochloride and 1.0 mg PLP (pyridoxal 5′-phosphate) were added, 0.1 M PB 7.0 was added until the final volume of the reaction solution was 1 mL, and 10 mg enzyme or immobilized transaminase prepared from 10 mg enzyme was added and stirred at 30° C. for 16 h. The transformation rate was measured by HPLC and reaction data are shown in Table 22 below.

TABLE 22 Reuse Transfor- times with Immobilization mation activity Strain number form Carrier rate (%) loss <5% Female parent No No 30.1 1 R416T + T7C + Covalent ECR8409 23.7 2 S47C immobilized ECR8285 17.6 2 enzyme A95P No No 67.3 1 Covalent ECR8409 47.7 4 immobilized enzyme R405E + K90G + No No 83.7 1 A95P + K304D + Covalent ECR8409 64.8 5 Q380L immobilized enzyme R405E + K90G + No No 97.5 1 A95P + K304D + Covalent ECR8409 92.3 5 Q380L + I297L immobilized enzyme R405E + K90G + No No 95.9 1 A95P + K304D + Covalent ECR8409 90.8 4 Q380L + H333K immobilized enzyme R405E + K90G + No No 96.7 1 A95P + K304D + Covalent ECR8409 93.1 4 Q380L + I297L + immobilized E368P + T107A enzyme R405E + K90G + No No 97.1 1 A95P + K304D + Covalent ECR8409 93.3 5 Q380L + I297L + immobilized E368P + T107A + enzyme A286T

Example 17: Reaction of Covalent Immobilized Transaminase in Organic Phase for Testing Activity

In a 10 mL reaction flask, 1 mL water-saturated isopropyl acetate was added, followed by 10 mg substrate 1 and 4 eq isopropylamine, then 20 mg enzyme or immobilized transaminase prepared from 20 mg enzyme was added, and stirred for 16 h at 30° C. The transformation rate was measured by HPLC and reaction data are shown in Table 23 below.

TABLE 23 Reuse Transfor- times with Immobilization mation activity Strain number form Carrier rate (%) loss <5% Female parent Covalent ECR8409 42.2 3 R416T + T7C + immobilized ECR8285 23.7 2 S47C enzyme A95P Covalent ECR8409 55.1 3 immobilized enzyme R405E + K90G + Covalent ECR8409 72.3 3 A95P + K304D + immobilized Q380L enzyme R405E + K90G + Covalent ECR8409 94.5 3 A95P + K304D + immobilized Q380L + I297L enzyme

Example 18: Continuous Reaction of Covalent Immobilized Enzyme in Transaminase Packed Bed (Methanol as Cosolvent for Substrate)

75 g immobilized enzyme prepared by mutant R405E+K90G+A95P+K304D+Q380L+1297L immobilized to ECR8409 carrier was filled into the reactor, the column volume (CV) was 150 mL, and 2CV buffer (0.1 M PB 7.0 containing 5 mg/mL PLP, 2 M isopropylamine hydrochloride) was injected into the packed bed with a plunger pump. The formulated reaction solution (0.5 M substrate 1, 2 M isopropylamine hydrochloride, 5 mg/mL PLP, 35% MeOH) was injected into a packed bed with a plunger pump, 40° C. water bath, a flow rate of 0.25 mL/min, retention time of about 600 min, transformation rate>98%, and a continuous operation for 240 h with no reduction in transformation rate.

Example 19: Glass Carrier Chelating Immobilized Transaminase

1 g EziG-101, EziG-102 or EziG-103 porous glass carriers were washed 1-2 times with buffer (20 mM Tris-Cl 8.5), the supernatant was removed, 20 mL Buffer was added to the carriers meanwhile enzyme powder or enzyme solution was added, stirred at 80 rpm for 1 h at 20° C., the supernatant was removed, the precipitate was washed 3-4 times with Buffer, filtered and dried under vacuum, and stored at 4° C.

Example 20: Reaction of Immobilized Transaminase Chelated on EziG-101 Porous Glass Carrier in Aqueous Phase for Testing Activity

In a 10 mL reaction flask, 0.2 mL DMSO was added, 0.1 g substrate 1 was dissolved, 4 eq isopropylamine hydrochloride and 0.5 mg PLP (pyridoxal 5′-phosphate) were added, 0.1 M PB 7.0 was added until the final volume of the reaction solution was 1 mL, and 0.1 g enzyme powder or immobilized transaminase prepared from 0.1 g enzyme powder by EziG-101 carrier chelating method was added and stirred at 45° C. for 16 h. The transformation rate was measured by HPLC and reaction data are shown in Table 24 below.

TABLE 24 Reuse Transfor- times with Immobilization mation activity Mutant form rate (%) loss <5% Female parent No 98.7 1 R416T + T7C + Chelating 98.2 4 S47C immobilized enzyme A95P No 98.5 1 Chelating 98.6 7 immobilized enzyme R405E + K90G + No 98.4 1 A95P + K304D + Chelating 98.2 11 Q380L immobilized enzyme R405E + K90G + No 98.5 1 A95P + K304D + Chelating 98.2 12 Q380L + I297L immobilized enzyme R405E + K90G + No 98.2 1 A95P + K304D + Chelating 98.0 12 Q380L + I297L + immobilized E368P + T107A + enzyme G201C R405E + K90G + No 98.2 1 A95P + K304D + Chelating 98.2 12 Q380L + I297L + immobilized E368P + T107A + enzyme A286T

Example 21: Reaction of Immobilized Transaminase Chelated on Porous Glass Carrier in Organic Phase for Testing Activity

In a 10 mL reaction flask, 1 mL water-saturated methyl tert-butyl ether was added, followed by 10 mg substrate 1 and 4 eq isopropylamine, then 20 mg enzyme or immobilized transaminase prepared from 20 mg enzyme was added, and stirred for 16 h at 30° C. The transformation rate was measured by HPLC and reaction data are shown in Table 25 below.

TABLE 25 Reuse Transfor- times with Immobilization mation activity Mutation site form Carrier rate (%) loss <5% Female parent Chelating EziG-101 69.8 4 R416T + T7C + immobilized EziG-102 59.9 3 S47C enzyme EziG-103 68.1 4 R405E + K90G + Chelating EziG-101 92.4 6 A95P + K304D + immobilized EziG-102 89.2 6 Q380L + I297L enzyme EziG-103 91.6 8

As can be seen from the above examples, the mutant with improved activity, stability, tolerance to temperature, pH and organic solvent obtained through directional evolution screening in the present application not only reduces the amount of enzyme used in production application, but also greatly improves the possibility of preparing various immobilized enzymes. In addition, in the present application by immobilizing (self-crosslinking or covalent bonding with a carrier) the transaminase subjected to directed evolution, the application of the immobilized transaminase in aqueous phase reaction and organic phase reaction is realized, so that the enzyme is easy to separate from a reaction system, the emulsification phenomenon caused by residual enzyme protein in the post-reaction treatment process is reduced, and meanwhile, the immobilized transaminase mutant can endure all kinds of extreme environment with low activity loss and high reuse times, thus realized the continuous transamination of substrate 1 and substrate 2.

The above are only preferred examples of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application. 

1. A transaminase mutant, wherein the transaminase mutant has an amino acid mutation sequence of SEQ ID NO:1, and sites of the amino acid mutation comprise T7C+S47C.
 2. The transaminase mutant according to claim 1, wherein the sites of the amino acid mutation further comprise any one or more of M356L, F364L, C404L, M430L, R405E/A, K90G, K219T, K304D, K51R, A95P, E368P, Q346E, H333K, D371G, E246A, C328A, N412G, T402P, T107F/A, G110P, K69N, G201C, Q380L, K193I, I297L, R305H, F111Y, K190E and A286T, wherein “/” represents “or”.
 3. The transaminase mutant according to claim 1, wherein the sites of the amino acid mutation further comprise any of the following combination mutant sites: K51R+W187Y, R405E+A95P, R405E+A95P+K304D, R405E+A95P+K304D+Q380L, R405E+K90G+A95P+K304D+Q380L, R405E+K90G+A95P+K304D+Q380L+E368P, R405E+K90G+A95P+K304D+Q380L+Q346E, R405E+K90G+A95P+K304D+Q380L+H333K, R405E+K90G+A95P+K304D+Q380L+D371G, R405E+K90G+A95P+K304D+Q380L+E246A, R405E+K90G+A95P+K304D+Q380L+C328A, R405E+K90G+A95P+K304D+Q380L+N412G, R405E+K90G+A95P+K304D+Q380L+T402P, R405E+K90G+A95P+K304D+Q380L+T107F, R405E+K90G+A95P+K304D+Q380L+T107A, R405E+K90G+A95P+K304D+Q380L+G110P, R405E+K90G+A95P+K304D+Q380L+I297L, R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A, R405E+K90G+A95P+K304D+Q380L+I297L+A286T, R405E+K90G+A95P+K304D+Q380L+I297L+E368P, R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+K69N, R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+G201C and R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T.
 4. A DNA molecule, wherein the DNA molecule encodes the transaminase mutant according to claim
 1. 5. A recombinant plasmid, wherein the recombinant plasmid is linked with the DNA molecule according to claim
 4. 6. An immobilized transaminase, wherein the immobilized transaminase comprises the transaminase mutant according to claim
 1. 7. The immobilized transaminase according to claim 6, wherein the immobilized transaminase is a transaminase cross-linked enzyme aggregate of the transaminase mutant; preferably the transaminase mutant is precipitated to obtain a transaminase aggregate, and a free amino, a phenolic, an imidazolyl, or a sulfhydryl in the transaminase aggregate is crosslinked with a cross-linking agent to obtain the transaminase cross-linked enzyme aggregate, wherein the cross-linking agent is selected from any one of glutaraldehyde, N, N-methylene biacrylamide, bismaleimide and dextran; preferably a molecular weight of the dextran is 6 KDa˜200 KDa; preferably the transaminase mutant is precipitated by ethanol to obtain the transaminase aggregate; preferably a free amino group in the transaminase aggregate is cross-linked with glutaraldehyde to obtain the transaminase cross-linked enzyme aggregate.
 8. The immobilized transaminase according to claim 6, wherein the immobilized transaminase is a transaminase embedded-crosslinked immobilized enzyme; preferably a free amino group in the transaminase mutant and glutaraldehyde form a Schiff base through crosslinking to obtain a transaminase cross-linked enzyme, the transaminase cross-linked enzyme is embedded into a polyacrylamide gel grid to obtain the transaminase embedded-crosslinked immobilized enzyme.
 9. The immobilized transaminase according to claim 6, wherein the immobilized transaminase is a covalent immobilized enzyme in which the transaminase mutant is covalently connected with a carrier; preferably the carrier is a chitosan carrier or a resin carrier; more preferably the chitosan carrier is covalently bound to the transaminase mutant through a hydroxyl and/or an amino group to form the covalent immobilized enzyme; more preferably the resin carrier comprises a matrix and a functional group connected with the matrix, wherein the matrix is selected from any of a styrene and methacrylate copolymer, a polystyrene resin and a polymethacrylate resin, and the functional group connected with the matrix is selected from a C2 short-chain amino group, a C4 medium chain amino group, and a C6 long-chain amino group or a epoxy group; further preferably the resin carrier is selected from ECR8309, ECR8315, EC-HFA, LX-1000HA, LX-1000EA, ECR8409, ECR8415, EC-EP, EC EP403, EXE119, LX-1000EP, Immobead-150A, Immobead-150P, Immobead350A, ECR8206, ECR8209, ECR8215 or ECR8285.
 10. The immobilized transaminase according to claim 6, wherein the immobilized transaminase is a chelating immobilized enzyme formed by chelating a transaminase mutant and a carrier through metal ions; preferably the carrier is a porous glass carrier; further preferably the porous glass carrier is EziG-101, EziG-102 or EziG-103.
 11. The immobilized transaminase according to claim 6, wherein the immobilized transaminase is an adsorptive immobilized enzyme formed by physical adsorption between the transaminase mutant and the carrier; preferably the carrier is a resin carrier; more preferably the resin carrier comprises a matrix and a functional group connected with the matrix, wherein the matrix is selected from any of a styrene and methacrylate copolymer, a polystyrene resin and a polymethacrylate resin, and the functional group connected with the matrix is an octadecyl; further preferably the resin carrier is selected from ECR8806, ECR1030, ECR1090, ECR1061, ECR1091, ECR8804, Immobead-EC1, Immobead-S60S, Immobead-S861, X17S0409, EXE120 or Diaion HP2MG.
 12. A method for producing a chiral amine, comprising a step of transamination reaction between a ketone compound and an amino donor catalyzed by a transaminase, wherein the transaminase is the transaminase mutant according to claim
 1. 13. The method according to claim 12, wherein the transaminase is the transaminase mutant according to claim 1, and the method is a batch reaction; preferably a reaction system of the batch reaction is an aqueous phase reaction system.
 14. The method according to claim 12, wherein the transaminase is the immobilized transaminase according to claim 6, and the method is a continuous reaction; preferably a reaction system of the continuous reaction is an organic phase reaction system.
 15. The method according to claim 12, wherein the ketone compound is

wherein R₁ and R₂ are each dependently a C1˜C8 alkyl, a C5˜C10 cycloalkyl, a C6˜C10 aryl or a C5˜C10 heteroaryl, or R₁ and R₂ together with the carbon on a carbonyl form a C5˜C10 heterocyclyl, a C5˜C10 carbocyclyl or a C5˜C10 heteroaryl, one or more of heteroatoms in the C5˜C10 heterocyclyl and C5˜C10 heteroaryl are respectively selected from at least one of nitrogen, oxygen and sulfur, and the aryl in C6˜C10 aryl, the heteroaryl in C5˜C10 heteroaryl, the carbocyclyl in the C5˜C10 carbocyclyl or the heterocyclyl in the C5˜C10 heterocyclyl is independently unsubstituted or substituted by at least one radical of halogen, alkoxy or alkyl; preferably the ketone compound is

wherein a product of the transamination reaction is

preferably the amino donor is isopropyl amine.
 16. The immobilized transaminase according to claim 7, wherein the transaminase cross-linked enzyme aggregate is a cross-linked enzyme aggregate of a transaminase mutant comprising the following amino acid mutation sites on the basis of the amino acid sequence shown in SEQ ID NO:1: T7C+S47C, T7C+S47C+A95P, T7C+S47C+R405E+K90G+A95P+K304D+Q380L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+K69N, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+H333K, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+E368P, T7C+S47C+K51R+W187Y, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+Q346E, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+C328A and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L.
 17. The immobilized transaminase according to claim 8, wherein the transaminase embedded-crosslinked immobilized enzyme is an embedded crosslinked immobilized enzyme of the transaminase mutant comprising the following amino acid mutation sites on the basis of the amino acid sequence shown in SEQ ID NO:1: T7C+S47C, T7C+S47C+R405E+K90G+A95P+K304D+Q380L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+Q346E, and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L.
 18. The immobilized transaminase according to claim 9, wherein the covalent immobilized enzyme is a covalent immobilized enzyme of the transaminase mutant comprising the following amino acid mutation sites on the basis of the amino acid sequence shown in SEQ ID NO:1: T7C+S47C, T7C+S47C+A95P, T7C+S47C+Q380L, T7C+S47C+R405E, T7C+S47C+K51R+W187Y, T7C+S47C+R405E+A95P+K304D, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+E368P, T7C+S47C+R405E+K90G+A95P+K304D+Q380L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+H333K, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T.
 19. The immobilized transaminase according to claim 10, wherein the chelating immobilized enzyme is a chelating immobilized enzyme of the transaminase mutant comprising the following amino acid mutation sites on the basis of the amino acid sequence shown in SEQ ID NO:1: T7C+S47C, T7C+S47C+A95P, T7C+S47C+R405E+K90G+A95P+K304D+Q380L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+G201C and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T.
 20. The immobilized transaminase according to claim 11, wherein the adsorptive immobilized enzyme is an adsorptive immobilized enzyme of the transaminase mutant comprising the following amino acid mutation sites on the basis of the amino acid sequence shown in SEQ ID NO:1: T7C+S47C, T7C+S47C+A95P, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+H333K. T7C+S47C+R405E+K90G+A95P+K304D+Q380L+Q346E, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+N412G, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A, T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+A286T and T7C+S47C+R405E+K90G+A95P+K304D+Q380L+I297L+E368P+T107A+G201C. 